NEW YORK — More than 1,000 hard-to-manage inmates ages 18 to 21 will be moved to a single Rikers Island facility by the end of the year and will be required to take hours of classes, receive counseling and be exempt from solitary confinement.

The plan, to be detailed publicly before the jail oversight board Tuesday, comes as officials continue to be frustrated by increased levels of violence across the lockups. It departs from a long-standing practice of housing young adult inmates among more hardened, experienced prisoners — and builds on an inmate management strategy commonly used in juvenile jails across the country to promote and reward good behavior.

“We strongly believe that the 18- to 21-year-old brain is about the same” as a juvenile’s, Jails Commissioner Joseph Ponte told The Associated Press in an interview this week. “I’m very confident that this model will work well for us in New York.”

The new young adult housing plan was born in part out of a series of mandated reforms by city jail watchdogs and federal prosecutors, who this summer reached a settlement agreement with corrections officials after suing over pervasive violence in the jails. That deal, combined with a change in state law, requires, among other things, separating 18-year-old inmates from 16- and 17-year-olds.

Ponte said he included inmates ages 19 to 21 in the housing plan because neuroscientists say that the brain isn’t fully formed until age 25 and that subjecting young adult inmates to 23-hour isolation to punish bad behavior is harmful. About 50 young adult inmates are now in solitary confinement, down from 162 when Ponte was appointed last spring, officials said.

Other lockups around the country, including in Florida, Maine and Massachusetts, have facilities exclusively for inmates who are 18 to 25.

Experts say young adult inmates are a particularly difficult population to manage.

At Rikers, about 400 of the 1,200 18- to 21-year-old inmates are gang members, responsible for about 34 percent of inmate assaults where a weapon is used, though they make up just 12 percent of the roughly 10,000 inmates in the jail system, according to jail statistics.

Overall there have been 98 stabbings and slashings so far this year — nine more than in all of 2014, the statistics show.

Union officials have argued that eliminating solitary will result in more violence. And Norman Seabrook, president of the union representing 9,000 city jail guards, said he also worried that correction officials haven’t briefed officers in detail about the programs to be offered in the new facility.

“Everything is top secret,” he said. “And I think that’s where these things fall apart.”

Funded with $12 million this year for programs plus millions more from health and education officials, the plan is essentially aimed at reducing the amount of time inmates spend with nothing to do.

Using an overhauled classification tool that measures an inmate’s dangerousness with data such as age, gang affiliation and police records, officials will place similarly situated inmates in units where they’ll get a minimum of five hours of behavioral therapy plus extra programs to study for practical accreditations, such as Occupational Safety and Health Administration certification.

Those units will be staffed according to court-mandated ratios, requiring two correction officers per 25 inmates in units for the most dangerous prisoners. By mixing certain rival gang members in such units, officials have found they’re able to force a balance of power that keeps the peace, Ponte said.

Officers in the new facility will be instructed to immediately take away privileges, such as extra recreation time or trips to the commissary, for bad behavior. Hard-to-manage inmates will in some cases get one-on-one supervision during outbursts in a more secure unit, Ponte said. And counselors will be charged with building rapport with the inmates to help connect them to programs that may help after they’re released.

Ponte said a pilot program of the new housing plan in one unit this summer has seen no fights or use of force by jail guards.

“It’s been so nearly perfect, it’s scary,” Ponte said, adding that the new endeavor has required “a lot of money, a lot of time, a lot of staff” and even more coaching.